It is now widely recognized that the generation of protective immunity depends not only on exposure to antigen, but also the context in which the antigen is encountered. Numerous examples exist in which introduction of a novel antigen into a host in a non-inflammatory context generates immunological tolerance rather than long-term immunity whereas exposure to antigen in the presence of an inflammatory agent (adjuvant) induces immunity. (Mondino et al., Proc. Natl. Acad. Sci., USA 93:2245 (1996); Pulendran et al., J. Exp. Med. 188:2075 (1998); Jenkins et al., Immunity 1:443 (1994); and Kearney et al., Immunity 1:327 (1994)). Since it can mean the difference between tolerance and immunity, much effort has gone into discovering the “adjuvants” present within infectious agents that stimulate the molecular pathways involved in creating the appropriate immunogenic context of antigen presentation.
CD27 is a member of the tumor necrosis factor receptor (TNFR) super family which also includes TNFR type I and II (CD120a and b), nerve growth factor receptor (NGFR), CD30, Fas/Apo-1 (CD95), CD40, 4-1BB and OX40. These proteins are known to play key roles in cell growth, survival, and differentiation as well as apoptosis or programmed cell death. Homology among these family members is restricted to the extracellular region and is characterized by the presence of a cysteine knot motif which occurs three times in CD27 (McDonald et al., Cell 73:4121-424 (1993)).
CD27 is a glycosylated, type I transmembrane protein of about 55 kilodaltons and exists as homodimers with a disulfide bridge linking the two monomers. The disulfide bridge is in the extracellular domain close to the membrane (Camerini et al., J. Immunol. 147:3165-69 (1991)). The ligand for CD27, CD70, belongs to the TNF family of ligands. CD70 is a type II transmembrane protein with an apparent molecular weight of 50 kd (Goodwin et al., Cell 73:447-456 (1993)). Based on homology to TNF alpha and beta, CD70 was predicted to have a trimeric structure made up of three identical subunits which interact with three CD27 homodimers (Peitsch et al., Mol. Immunol. 152:1756-1761 (1994)). TNF alpha which also is a type II transmembrane protein, is released from the cell by proteolytic cleavage, whereas TNF beta and NGF are secreted.
CD27 and its ligand CD70 are expressed on discrete populations of T and B cells. CD27 is expressed on resting T cells and CD70 on activated T and B cells and dendritic cells. Within T cell subsets, CD27 is stably expressed on CD45RA+ cells even after activation, whereas on CD45RO+ cells it is weakly expressed and lost after activation. (Sugita et al., J. Immunol. 149:3208-3216 (1992); Hintzen et al., J. Immunol. 151:2426-2435 (1993)). On CD45RA+ cells, activation by various means results in the upregulation of CD27 expression (Hintzen et al., J. Immunol. 151:2426-2435 (1993)). CD27 is highly expressed on most of the B cell non-Hodgkin's lymphomas and B cell chronic lymphocytic leukemias. (Ranheim et al., Blood 85:3556-3565) The B cell lines Ramos and Raji, also express significant levels of CD27 and CD70.
Ligation of CD27 along with treatment of T cells with sub-optimal dose of PMA, PHA, anti-CD2 or anti-CD3 antibodies is also known to result in the proliferation of T cells, thus defining a co-stimulatory role for CD27. It has also been reported that CD27-mediated co-stimulatory effects can be specifically inhibited using an anti-CD27 antibody or recombinant soluble CD27 or anti-CD70 antibody and that ligation of CD27 via its ligand, CD70 can generate cytolytic T cells. (Goodwin et al., Cell 73:447-456 (1993)).
Another co-stimulatory molecule which is known to regulate adaptive immunity is CD40. CD40 is a member of the TNF receptor superfamily and is essential for a spectrum of cell-mediated immune responses and required for the development of T cell dependent humoral immunity (Aruffo et al., Cell 72:291 (1993); Farrington et al., Proc Natl Acad. Sci., USA 91:1099 (1994); Renshaw et al., J Exp Med 180:1889 (1994)). In its natural role, CD40-ligand expressed on CD4+ T cells interacts with CD40 expressed on DCs or B cells, promoting increased activation of the APC and, concomitantly, further activation of the T cell (Liu et al Semin Immunol 9:235 (1994); Bishop et al., Cytokine Growth Factor Rev 14:297 (2003)). For DCs, CD40 ligation classically leads to a response similar to stimulation through TLRs such as activation marker upregulation and inflammatory cytokine production (Quezada et al. Annu Rev Immunol 22:307 (2004); O'Sullivan B and Thomas R Crit. Rev Immunol 22:83 (2003)) Its importance in CD8 responses was demonstrated by studies showing that stimulation of APCs through CD40 rescued CD4-dependent CD8+ T cell responses in the absence of CD4 cells (Lefrancois et al., J. Immunol. 164:725 (2000); Bennett et al., Nature 393:478 (1998); Ridge et al., Nature 393:474 (1998); Schoenberger et al., Nature 393:474 (1998). This finding sparked much speculation that CD40 agonists alone could potentially rescue failing CD8+ T cell responses in some disease settings (French et al., Nature Medicine 1999).
Other studies, however, have demonstrated that CD40 stimulation alone insufficiently promotes long-term immunity. In some model systems, anti-CD40 treatment alone insufficiently promoted long-term immunity, i.e., yields ineffective inflammatory cytokine production. as well as the deletion of antigen-specific T cells (Mauri et al. Nat Med 6:673 (2001); Kedl et al. Proc Natl Acad. Sci., USA 98:10811 (2001)) and termination of B cell responses (Erickson et al., J Clin Invest 109:613 (2002)). Also, soluble trimerized CD40 ligand has been used in the clinic as an agonist for the CD40 pathway and what little has been reported is consistent with the conclusion that stimulation of CD40 alone fails to reconstitute all necessary signals for long term CD8+ T cell immunity (Vonderheide et al., J Clin Oncol 19:3280 (2001)).
Both agonistic and antagonistic antibodies specific to CD40 have been suggested to have potential as human therapeutics. Antagonistic anti-CD40 antibodies include those that (1) block CD40/CD40L interaction by at least 90% and have purported antineoplastic properties (Armitage et al., U.S. Pat. No. 5,674,492; Fanslow et al., 1995, Leukocyte Typing V Schlossman et al., eds., 1:555-556); (2) those that antagonize signaling through CD40 (deBoer et al., U.S. Pat. No. 5,677,165) and (3) those that deliver a stimulatory signal through CD40 but do not increase the interaction between CD40 and CD40L, e.g., G28-5, (Ledbetter et al., U.S. Pat. No. 5,182,368; PCT WO 96/18413).
Agonistic anti-CD40 antibodies have been reported by several groups. For example, one mAb, CD40.4 (5C3) (PharMingen, San Diego, Calif.) has been reported to increase the interaction between CD40 and CD40L by approximately 30-40% (Schlossman et al., eds., Leukocyte Typing, 1995, 1:547-556). Additionally, Seattle Genetics in U.S. Pat. No. 6,843,989 allege to provide methods of treating cancer in humans using anti-human CD40 antibodies. These antibodies are alleged to deliver a stimulatory signal, to enhance the interaction between CD40 and CD40L by at least 45% and to enhance CD40L-mediated stimulation and to possess in vivo neoplastic activity. The exemplified antibody disclosed in the Seattle Genetics patent was derived from S2C6, an agonistic anti-human CD40 antibody previously shown to deliver strong growth-promoting signals to B lymphocytes (Paulie et al., 1989, J. Immunol. 142:590-595).
However, notwithstanding these prior reports, improved methods and human therapies using adjuvants that promote Th1 immunity and which enhance the activation and expansion of antigen specific CD8+ T cells, i.e. CD8+ effector and memory cells are needed. Particularly, improved methods of treating human cancer and other diseases using therapeutic adjuvants which are safe and effective, i.e., which do not elicit undesired side effects but which elicit substantial therapeutic effects, e.g., anti-tumor effects are needed. The present invention satisfies this need and provides other advantages as well.